The discovery of the Toll-Like Receptor Proteins (TLRs) and their importance in the regulation of host response to infection has led to a series of investigations related to the role of host proteins and cytokines in microbial pathogenesis. Recent work has demonstrated that not only do these TLRs function as cell surface receptors for foreign antigens, but also that TLRs (especially TLR 3, 7, 8 and 9) are endosomally localized and they recognize infectious agents (particularly viruses and viral nucleic acids). In addition to the TLRs, the production of type 1 interferons (IFNs) has been shown to be regulated by cytoplasmic RNA helicase proteins, like RIG-I and Mda-5, and by inflammosame proteins like NLRP-3 (or NALP-3, Cryopyrin) which are related to the NOD family of proteins. Several Interferon Regulatory Factors (IRFs), which control the production of type I IFNs, have been implicated downstream of these different viral sensing pathways. The overall hypothesis of the Project is that pattern recognition proteins respond to particular viral antigens and that those responses are regulated by other viral proteins and it is the effect of the host cytokines induced as a result of this interaction that determines the pathogenic potential of a virus. Project 1 (Kurt-Jones) will define the role of TLRs in HSV induced inflammatory responses and viral pathogenesis and how IRF-1 signaling regulates these responses. Project 2 (Fitzgerald) will define the role of IL-I, NLRP-3, and TLR-independent DNA sensors in the virus-induced production of inflammatory cytokines and type I interferons, and the control of anti-viral immunity. Project 3 (Knipe) will define how certain viral proteins regulate TLR signaling and TLR adapters (and other pattern recognition proteins) and affect the secretion of interferon and cytokines. Project 4 (Finberg) will examine how recently defined polymorphisms in TLRs and other host genes important in innate immunity, affect reactivation of HSV. All Projects involve the use of common reagents and the definition of new paradigms related to recognition and response of the host to HSV. PROJECT 1: TLRs and IRF1 in the Innate Immune Responses to HSV-1 (Kurt-Jones, E) PROJECT 1 DESCRIPTION (provided by applicant): The innate immune response is the first line of defense against viral pathogens. In the absence of an antiviral innate response, viral replication is uncontrolled and lethal disseminated infection can occur. Pattern recognition receptors (PRRs) are critically involved in the development of innate anti-viral immunity. Innate immune activation by viruses may occur via cell surface, intracellular and/or cytosolic pattern recognition receptors. These receptors may sense different viral components and may activate unique downstream pathways to generate anti-viral immunity. We hypothesize that PRR interaction with herpes viruses activates IRF1-dependent downstream pathways in innate immune cells that are critically involved in the control of the inflammatory response to HSV infection. In this project, we will;1. Define the role of TLRs in HSV innate immune responses 2. Define the mechanism of IRF1 regulation of innate immunity and protection from lethal HSV encephalitis 3. Define the role of HSV in TLR signaling and IRF1 activation of pro- and anti-inflammatory anti-viral pathways. We will define the PRRs, particularly TLRs that sense HSV infection and trigger innate immune responses. We will define the mechanism of IRF1 regulated HSV responses by defining the receptors and mediators upstream of IRF1 activation as well as the target genes and factors downstream of IRF1 in HSV infection. These studies are complemented by studies of Dr. Fitzgerald (Project 2) examining a unique intracellular virus sensing pathway that is also dependent on IRF1. We will utilize pathway specific reagents generated by Dr. Fitzgerald as well as viruses and viral mutants generated by Dr. Knipe (Project 3) to define the mechanisms of PRR-virus interactions leading to IRF1 activation. The role of PRR pathways in HSV immunity will be extended to human patients by studies conducted by Dr. Finberg (Project 4). These studies will further the overall goals of the Program Project by defining the cells, receptors and viral components that are critically involved in the initiation of viral immunity and protection of the host from lethal encephalitis.